In VDSL systems, one of the major factors in limiting rates comes from self-FEXT (self-induced far-end crosstalk). Generally, devices for mitigating self-FEXT are CO-centric and require signal cooperation, also known as signal vectoring, across the different ports that are involved in an aDSM-3 session. Vectoring enables the CO (central office) to access transmit and receive symbols of the vectored users. Therefore, FEXT cancellation in both the upstream and downstream directions is generally performed at the CO. However, the computing resources available can be limited and therefore, the level of complexity of computations that the CO can process is limited.
Suppose that N represents the number of vectored users. A full, self-FEXT cancellation scheme requires computations of the order (N2) per DMT symbol period. Note that the total number of tones engaged is nearly 4,096 and with just 10 vectored users, the complexity level for total self-FEXT cancellation is on the order of billions of flops per second. Moreover, the power dissipation in the FEXT mitigation devices is also proportional to the complexity of the FEXT mitigation algorithm. Those skilled in the art will appreciate that such a degree of complexity involved in any full self-FEXT cancellation cannot be met with the present day availability of silicon. As such, there is a need for optimal utilization of available computational resources at the central office in order to perform self-FEXT mitigation and enhance data rates.